Experience with a Vehicle Energy Audit Using Tire Pressure and Exhaust Gas Analysis 922386

The Alberta Department of Energy has developed a four part Transportation Energy Audit program. The full program incorporates vehicle selection, route planning, driver training, and vehicle maintenance phases. This paper discusses the background and experience using the vehicle maintenance phase.

Vehicle maintenance condition is assessed using a simple inspection procedure based on tire pressure and tailpipe exhaust emissions at idle and fast-idle conditions. With these measurements, vehicles are ranked in order of maintenance condition and estimates are made of the potential fuel cost savings obtainable by improved maintenance. Tire under-inflation is converted to potential fuel cost savings using an equation based on tire rolling resistance properties, inflation pressure, and the relative importance of tire rolling resistance in total vehicle fuel consumption. Vehicle tailpipe emissions (for spark ignition engines only) are converted to potential fuel savings using an equation developed from EPA emission factor test data. The measured emissions are compared with an expected value from a set of tables which allows for vehicle type, model year, and accumulated mileage using accepted deterioration rates. This avoids discriminating unnecessarily against large, old, or high mileage vehicles while making a realistic estimate of potential for improvements.

When applied to fleets of similar vehicles, this procedure is a simple and cost effective way of showing fleet managers the relative condition of their vehicles. The fuel cost savings estimates help to quantify the benefits of improved maintenance and the trade-off against maintenance or repair costs. The paper discusses experience with application to vehicle fleets and to a general vehicle population at voluntary emissions clinics.